Starch is a very commonly used material in a number of technical and industrial applications including, for example, in the production of building materials, the manufacture of paper, the treatment of textiles, the preparation of adhesives and the formulation of products such as detergent tablets or pharmaceuticals. They are also used in a variety of food applications as thickeners, binders, emulsifying agents and gelling agents, for instance.
Starch is a pseudo-crystalline material consisting of two polymers of alpha-D-glucose: amylose and amylopectin. Amylose is essentially a linear polymer in which glucose molecules are bound through alpha 1-4 bonds while amylopectin is a branched polymer containing both alpha 1-4 and 1-6 linkages.
Depending on its required use and functionality, the nature and structure of the starch molecule may have to be modified. This can be achieved by a number of techniques including thermal, chemical and enzymatic treatment.
In most applications, starch is used in the form of a gelatinised paste. Depending on the modifications performed, and its desired end use, the starch paste will have a higher or lower viscosity.
When a low viscosity is required, starch molecules are usually submitted to a process known as thinning. Thinning can be carried out in the wet phase (where water is used as a vehicle for the reactants) or in the dry phase (characterised by the absence of a solvent medium).
Examples of wet phase thinning include acid-modification and oxidation. Both must be carried out below the gelatinization temperature of the starch and have relatively long reaction times. The reaction slurry must have a pH which is adjusted to a more or less neutral value and, after the thinning process has been completed, it must be washed to remove salts which are used to inhibit gelatinization.
A key limitation of this wet technology is the amount of water that is wasted and the costs associated with its treatment before disposal.
A number of dry processes have therefore been proposed. For instance, EP0710670 (Vomm Impianti e Processi S.r.L.) describes a continuous chemical modification process by which a starch powder and a modification agent, for example a hydrolytic agent or an alkylation agent, are introduced simultaneously into a thermostatically controlled turbo-reactor comprising a propeller rotating at 300-1500 revolutions per minute. This device enables, almost instantaneously, the creation of a fluid, fine, dynamic and highly turbulent layer of a close mix between the starch particles and the chemical agent.
With such a device, the chemical modification of starch can be carried out in much shorter time. For instance, Example 1 of the patent describes the hydrolysis at 50° C. of a maize starch by hydrochloric acid wherein the retention time of the starch in the reactor is only about 30 seconds. Unfortunately, this process requires the use of a specific device which, in addition to its high energy requirements, naturally increases production costs.
To overcome these drawbacks, EP0902037 (Roquette Frères) proposes a process for thinning starch under acidic conditions. The process is continuous with a reaction time of at least 5 minutes at 60 to 100° C.
Thus, although it is easier to obtain thinned starch with this process than by using a specific turbo-reactor, the processing time is longer and productivity is therefore reduced. In addition, a costly heating step is necessary to bring the temperature to the required 60-100° C.
It is therefore apparent that an improved process for the manufacture of thinned starch is desired. It is an object of the present invention to provide such a method.